Background:
An accessory lobe is a part of lung tissue separated off by an
accessory fissure. It develops due to occasional monopodial branching
of the stem bronchi. Different accessory lobes may be encountered in
the human lungs e.g., azygos lobe, dorsal lobe, cardiac lobe and
tracheal lobe. An accessory lobe may be confused with a lung abscess or
bulla in x-ray and CT-scan, and its variable bronchial supply may cause
difficulty during bronchoscopy. Hence, the present work has been
carried out to study the accessory lobes and their bronchial branching
pattern in human lungs. Materials
and Methods: 92 adult human lungs (46 right and 46 left)
were collected from the Department of Anatomy and Department of
Forensic and State Medicine, Gauhati Medical College and Hospital,
Guwahati, Assam and preserved in 10% formalin. The lungs were, then,
examined for accessory lobes and their bronchial supply was noted
following dissection from the hilum. Results: In the
present study, the azygos lobes were present in 2.17% of cases and
dorsal lobe was present in 1.08% of cases, all of which belonged to the
right side. The azygos lobes were supplied by the apical segmental
bronchus of the right superior lobe and dorsal lobe was supplied by the
apical basal segmental bronchus and posterior basal segmental bronchus
of the right inferior lobe. Conclusion:
A detailed knowledge of the accessory lobes and their bronchial supply
is important for correct radiological diagnosis and bronchoscopic
examination of lungs.

An accessory lobe of lung is a part of it, separated off by an
accessory fissure, a cleft of variable depth in the lung tissue, lined
by visceral pleura [1]. During development, accessory bronchi and lobes
of lung develop as a result of occasional monopodial branching of the
stem bronchi [2].

Several accessory lobes are described in the literature. When the
medial part of the upper lobe of the right lung is separated off by a
fissure containing the terminal part of the azygos vein, it is called
the ‘lobe of the azygos vein’ or azygos lobe [3].
The fissure separating the azygos lobe is called the azygos fissure
[4]. The azygos fissures may vary in depth and may cut the lateral
surface of the lung between the apex and a point two inches below the
apex, or may divide the apex of the lung into lateral halves, or may
cut off a small tongue shaped lobe from the mediastinal surface of the
lung [3,5]. The azygos lobes may also vary in size [3]. They develop
when the apical bronchus, instead of growing lateral to the arch of the
azygos vein, grows medial to it [6]. As a result, the azygos vein lies
in the free margin of a mesentery formed by the mediastinal pleura,
called the ‘mesoazygos’ [3,7]. The azygos lobes may
also occur on the left side, when a fissure containing the left
superior intercostal vein or ‘vena azygos minor’ is
present on the left upper lobe [5].

Among other accessory lobes, a posterior lobe or dorsal lobe may be
found in the lung, which is the superior segment of the lower lobe,
separated off by the superior accessory fissure, from the basal
segments. Sometimes, an inferior accessory lobe or cardiac lobe may be
present in the lung, which is the medial basal segment of the lower
lobe, separated off by the inferior accessory fissure, from the rest of
the lower lobe [1,8]. Tracheal lobe is the type of accessory lobe,
arising from the trachea itself through an accessory bronchus and is
located in the upper part of the thorax [9].

An azygos fissure may produce ‘tear drop effect’ in
a chest x-ray, in which the cleft between the ‘lobe of the
azygos vein’ and superior lobe of the lung is represented by
a thin line, into which the pleura dipped to enclose the vein [10].
Radiologically, an azygos lobe may be mistaken for a lung abscess or
bulla [11]. Knowledge of their bronchial supply also helps in proper
therapeutic drainage of secretions from the lungs [7]. Rarely, the
azygos lobes may be associated with recurrent hemoptysis without any
obvious cause and primary lung carcinoma [12,13]. Moreover, variations
of the lung lobes and their bronchial branching may cause difficulties
during bronchoscopic examination, and a tracheal bronchus, leading to a
tracheal lobe, may cause recurrent respiratory tract infection in
infants [6,14].

Hence, the present work has been carried out to study the accessory
lobes and their bronchial branching pattern in human lungs.

Materials
and Methods

Type of study: Descriptive
study.Place of study: Department
of Anatomy, Gauhati Medical College and Hospital, Guwahati, Assam.Duration of study:
August 2015 to September 2016.Sample size:
92 lungs (46 right and 46 left).

Sample collection:
The lungs were collected from the Department of Anatomy and Department
of Forensic and State Medicine, Gauhati Medical College and Hospital,
Guwahati, after obtaining ethical clearance from the Institutional
Ethical Committee.

Method:
After collection, the lungs were washed in running tap water and
preserved in 10% formalin. Lungs were then observed for accessory lobes
and their bronchial supply was noted after breaking the surface at the
hilum, and scrapping away the alveolar tissues from the bronchi,
arteries and veins, following Cunningham’s manual of
practical anatomy [15]. The lengths of the accessory fissures were
measured using a thread and external jaws of a Vernier caliper and
their maximum depths were measured using the depth measuring blade of
the caliper, and then the average length and depth were calculated.

Statistical methods:
Tabulation and analysis of the data was done in Microsoft Excel sheets.

Results

In the present study, out of 92 lung specimens, the azygos lobes were
present in two right lungs (2.17%) (Table: 1). In all the lungs, the
azygos lobes were tongue shaped and separated from the mediastinal
surfaces by the azygos fissures (Fig: 1). They were present medial to
the superior lobes and superior to the hila of the lungs. In one of the
lungs, the azygos lobe was larger than the other. In all the lungs, the
azygos lobes reached up to the apices and were supplied by the apical
segmental bronchi of the right superior lobes (Fig: 2). The average
length of the azygos fissure was 2.74 cm and average depth (maximum)
was 0.58 cm.

Table-1: Incidence of
accessory lobes of lungs

Lung

Accessory
lobe

Azygos lobe

Dorsal lobe

No. of specimens

%

No. of specimens

%

Right (n=46)

2

4.35

1

2.17

Left (n=46)

0

0

0

0

Figure-1:
Showing azygos lobe and azygos fissure in the right lung (medial
surface).

Figure-2: Showing
bronchial supply of azygos lobe in the right lung (medial surface).

Figure-4: Showing
bronchial supply of dorsal lobe in the right lung (lateral surface).

Moreover, out of 92 lung specimens, the dorsal lobe was present in one
right lung (1.08%) (Table: 1). In this lung, the dorsal lobe was
separated from the basal segments of the inferior lobe by the superior
accessory fissure (Fig: 3). The length of the superior accessory
fissure was 5.58 cm and depth (maximum) was 1.22 cm. It was supplied by
the apical basal segmental bronchus and posterior basal segmental
bronchus of the right inferior lobe (Fig: 4).

Discussion

Several authors have studied the accessory lobes of lungs and their
bronchial branching pattern. Mata quoted Boyden and Heitzman in his
article [16] as saying that the azygos lobes are present in 1% of
anatomic specimens and 0.4% of chest radiographs. Rauf et al [17], in a
cadaveric study, reported 0.57% of cases of azygos lobes, while Anson
et al [10] reported radiographic incidence of azygos lobes in 0.59% of
cases. Özdemir [18] reported 1.54% of cases of azygos lobes
and Crawford [19] reported 0.11% of cases of azygos lobes in computed
tomographic studies. However, in the present study, the incidence of
azygos lobes is higher (2.17%) than the previous studies.

Ashwini [20] and Radha [21] reported cases, where the azygos fissures
cut the apices of lungs into lateral halves, while Stibbe [5] described
cases, where the azygos fissures were present on the lateral surfaces
and medial surfaces of the apices of lungs. He also reported a case of
azygos lobe, where the azygos fissure was present on the medial surface
of the apex of lung, cutting a tongue shaped azygos lobe, which is
similar to the case found in the present study.

Bray quoted Wrisberg in his article [22] found that the azygos lobes
were present bilaterally, in the cadaver of a three year old boy.
Stibbe [5] also mentioned the occurrence of azygos lobes on the left
side. However, Takasugi and Godwin [23] reported higher incidence of
azygos lobes on the right side as compared to the left side. Rauf et al
[17], Ashwini [20] and Radha [21] also reported cases of azygos lobes
on the right side. In the present study, all the cases of azygos lobes
were present on the right side.

Stibbe quoted Cairney in his article [5] as saying that the azygos lobe
was supplied by a branch of the eparterial bronchus, which passed
medial to the branches supplying the apex of lung. Kobayashi et al
[24], Arakawa et al [7] and Kim et al [25] reported cases, where the
azygos lobes were supplied by the anterior and posterior branches of
the apical segmental bronchi, while Chiba et al [26] reported a case,
where the azygos lobe was supplied by the posterior branch of the
apical segmental bronchus and lateral branch of the posterior segmental
bronchus. Ndiaye et al [27] reported a case, where the azygos lobe was
supplied by the whole posterior branch of the apical segmental
bronchus. In the present study, the azygos lobes were supplied by the
apical segmental bronchus of the right superior lobe, which is similar
to the findings of Kobayashi et al [24], Arakawa et al [7] and Kim et
al [25].

Ando T quoted Dévé, Oppenheim and Oguro in his
article [28] found that 15% of cases of dorsal lobes (22% of cases on
the right side and 8% of cases on the left side) were present in an
adult European population, 17% of cases of dorsal lobes (15% of cases
on the right side and 19% of cases on the left side) were present in an
adult Chinese population and 6.5% of cases of dorsal lobes (10.86% of
cases on the right side and 2.17% of cases on the left side) were
present in an adult Japanese population respectively. Mawatari et al
[29] reported 6.96% of cases of dorsal lobes (12.93% of cases on the
right side and 2.55% of cases on the left side). However, in the
present study, the incidence of dorsal lobes is lower (1.08%) than the
previous studies and all belongs to the right side.

Ando T also quoted Dévé in his article [28] that
there were four types of dorsal lobes, depending on the completeness of
accessory fissures, separating the lobes, such as, (a) lower lobe
completely separated by the accessory posterior fissure, (b) lower lobe
separated incompletely by the accessory posterior fissure connecting
with other normal fissures, (c) lower lobe separated incompletely by
the accessory posterior fissure, without connection with the normal
fissures and (d) lower lobe separated incompletely by the accessory
posterior fissure, which exists as a traceable shallow groove. In the
present study, the dorsal lobe is incompletely separated by the
accessory posterior fissure or superior accessory fissure, which is
connected with other normal fissures.

Sreenivasulu et al [30] reported a case of dorsal lobe in the left
lung, which was supplied by the apical basal segmental bronchus and
posterior basal segmental bronchus. Mawatari et al [29] reported a
case, where the dorsal lobe was supplied by the medial basal segmental
bronchus forming a common trunk with sub superior bronchus or anterior
basal segmental bronchus. The bronchial supply of the dorsal lobe, in
the present study, is similar to the findings of Sreenivasulu et al
[30].

Conclusion

From the present study it can be concluded that, the incidence of the
azygos lobes and dorsal lobes of lungs, in the population of Assam,
varies with other populations. Moreover, there are few studies on the
accessory lobes of lungs and their bronchial branching pattern. Thus,
more studies have to be conducted, in this regard, for correct
radiological diagnosis and bronchoscopic examination of lungs.

What this study adds to
existing knowledge?
There were no previous anatomical studies on the accessory lobes of
lungs and their bronchial branching pattern from the North-Eastern
region (Assam) of India. Thus, it will help the radiologists and ENT
surgeons of this part of the world to know the different variations of
the lobes of lungs and their bronchial supply, and formulate management
strategies accordingly.

Contribution by different
authors- The study was conducted under able guidance of
Dr. Joydev Sarma, Vice Principal and Professor, Department of Anatomy,
Gauhati Medical College and Hospital, Guwahati, Assam. The manuscript
was jointly prepared by Dr. Satyajit Mitra, Associate Professor and HOD
(i/c), Department of Anatomy, Gauhati Medical College and Hospital,
Guwahati, Assam and Dr. Krishna Kanta Biswas, Demonstrator, Department
of Anatomy, Silchar Medical College and Hospital, Silchar, Assam.